This invention relates to field emission displays and more particularly to a technique for improving brightness and efficiency of field emission displays.
As it is known in the art, typically a conventional field emission display (FED) uses a triode structure with small cathode to anode spacing. The emitter and gate are integral to the matrix addressable field emission cathode and the anode is placed approximately 0.2 mm away. This spacing is maintained by small spacers placed between the cathode and anode. The problem with this structure is the small spacing limits the anode voltage to typically under 1000 volts which in turn limits brightness and efficiency. To operate at increased voltage, the cathode to anode spacing must be increased. However, the angular distribution of the electrons that are emitted from the cathode have a half angle of over thirty degrees such that as the spacing is increased, the electron beam from the pixels spread out with a loss of video resolution on the phosphor anode. The high voltage tends to curve the electron trajectories into lines more perpendicular to the anode surface but the latter is not enough to overcome the initial high angular spread. Another problem with a high voltage anode is that any positive ions created at the anode will be accelerated back to the cathode and cause damage.